<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="../js/vue.js"></script>
</head>
<body>
   
    <div id="root">
        姓: <input type="text" v-model="firstName"> <br>
        名: <input type="text" v-model="lastName"> <br>
        姓名: <span>{{firstName.slice(0,3)}}-{{lastName}}</span> <br>
      
    </div>
    
</body>
 
<script type="text/javascript">
    Vue.config.productionTip=false;

    new Vue({
        el:"#root",
        data:{
            firstName:'张',
            lastName:'三'
        }
    })
   
</script>
</html>